How Steel Mills Are Powering Furnaces with Their Own Emissions
In the heart of modern steelworks, a revolutionary cycle is turning waste into wealth and pollution into power.
The image of a steel mill often brings to mind fiery furnaces and billowing smokestacks. However, a quiet revolution is underway within these industrial giants, one that is making them both cleaner and more cost-effective. This transformation is centered on a once-overlooked byproduct: converter gas. Known technically as BOFG (Basic Oxygen Furnace Gas), this waste product of the steelmaking process is now being used as a valuable substitute for natural gas in massive tunnel furnaces, creating a circular economy that benefits both the environment and the bottom line. This innovative approach demonstrates that the path to industrial sustainability may not always require exotic new technologies, but rather the smarter utilization of the resources we already have.
The iron and steel industry is a cornerstone of modern civilization, but it comes with a significant environmental cost. It is estimated to consume 5–10% of global energy and accounts for approximately 4–7% of total anthropogenic CO₂ emissions1 3 . The industry faces relentless pressure to modernize its processes to meet stringent ecological and economic requirements1 .
Steel production accounts for 5-10% of global energy consumption and 4-7% of COâ‚‚ emissions.
Converter gas utilization turns waste into valuable fuel, creating a circular economy.
Traditionally, the steelmaking process generates several gaseous byproducts. Converter gas is produced when pure oxygen is blown onto molten iron in a basic oxygen furnace, a violent process that rapidly reduces carbon content and impurities4 . This process generates a gas that was often considered waste. Its composition varies but typically includes 56–70% carbon monoxide (CO), 13–20% nitrogen (N₂), 15–21% carbon dioxide (CO₂), and about 1–4% hydrogen (H₂)1 3 . With a relatively low calorific value of 8.0 to 9.0 MJ/Nm³, it was historically seen as inconvenient to manage and was sometimes simply flared—burned off into the atmosphere—representing both an economic loss and an unnecessary environmental burden1 .
The breakthrough came from a simple yet powerful idea: instead of releasing this gas, why not capture it and use it as a substitute for purchased natural gas in other parts of the steelworks? This concept of industrial symbiosis—where the waste of one process becomes the fuel for another—is the key to unlocking a more sustainable and profitable steel industry.
To validate the practical potential of this idea, researchers conducted a detailed theoretical analysis focused on implementing converter gas as the primary fuel for a tunnel furnace used to heat steel sheets for rolling or hardening1 . This section breaks down their innovative methodology and findings.
At the heart of this experiment was the need to accurately simulate the combustion of converter gas, a complex process involving numerous chemical reactions. The research team employed advanced computational techniques to model this phenomenon.
The researchers used a sophisticated model developed by Konnov to simulate the combustion chemistry. This mechanism offers a balanced approach, providing accuracy comparable to more detailed models but with much shorter computation times, making the analysis feasible1 .
This skeletal mechanism was obtained using the Directed Relation Graph with Error Propagation aided Sensitivity Analysis (DRGEPSA) method. This is a cutting-edge technique for simplifying complex chemical models without sacrificing critical predictive accuracy1 .
Before applying it to converter gas, the research team first validated their computational model on a real tunnel furnace that was known to be running on natural gas. This crucial step ensured that their simulations could reliably predict real-world outcomes1 .
The experiment was conducted as a theoretical simulation, following a rigorous process1 :
Defining the precise chemical composition of converter gas based on typical values.
Simulating combustion of both natural gas and converter gas in a virtual furnace model.
Calculating flue gas composition with focus on NO and COâ‚‚ pollutants.
Comparing market price of natural gas with internal cost of using converter gas.
The findings from this detailed simulation revealed a mixed but ultimately promising picture, highlighting both environmental trade-offs and significant net gains.
in Nitric Oxide (NO) emissions when switching from natural gas to converter gas.
From 275 ppm to 80 ppm
in Carbon Dioxide (COâ‚‚) emissions due to high inherent COâ‚‚ content in converter gas.
But this COâ‚‚ is produced regardless of gas utilization method
The most striking environmental benefit was the dramatic reduction in nitric oxide (NO) emissions, which fell from 275 parts per million (ppm) with natural gas to just 80 ppm with converter gas—a drop of over 70%1 . This is a significant improvement in air quality.
However, the analysis also revealed a challenge: carbon dioxide emissions increased more than threefold when using converter gas1 . This is due to the high inherent COâ‚‚ content in the gas before it is even burned. The researchers rightly point out that this COâ‚‚ is an unavoidable byproduct of the steel manufacturing process itself; whether the gas is flared or used as fuel, these emissions remain. The key is that by using it productively, the facility avoids the additional emissions that would have come from burning purchased natural gas1 .
by replacing purchased natural gas with internally captured converter gas1
The economic argument, however, was overwhelmingly positive. The economic analysis demonstrated substantial savings, with a 44% reduction in fuel purchase costs achieved by substituting expensive natural gas with the plant's own converter gas1 . This transforms a cost center (waste gas management) into a profit center (fuel generation).
| Tool or Concept | Function in the Research |
|---|---|
| Converter Gas (BOFG) | The subject fuel, a by-product of basic oxygen steelmaking, primarily composed of CO, COâ‚‚, and Nâ‚‚. |
| Skeletal Kinetic Mechanism | A simplified but accurate chemical model that predicts how fuel burns and what emissions form. |
| DRGEPSA Method | A sophisticated algorithm used to create the simplified skeletal kinetic mechanism from a more complex model. |
| Computational Fluid Dynamics (CFD) | Software that simulates the flow, heat transfer, and chemical reactions inside a furnace. |
| System Boundaries | Defining the scope of the analysis (e.g., from the gas source to the furnace stack) to ensure accurate and meaningful results. |
The successful deployment of converter gas in tunnel furnaces is part of a larger trend towards "deep decarbonization" in the steel industry, which contributes about 8% of global greenhouse gas emissions5 . Other promising strategies include shifting to electric arc furnaces powered by renewable energy and exploring the use of green hydrogen as a clean reducing agent instead of coal5 .
Powered by renewable energy sources to reduce carbon footprint.
As a clean reducing agent to replace coal in steel production.
Maximizing resource efficiency through waste utilization.
While these long-term solutions develop, the use of process gases like BOFG represents a crucial intermediate step. It demonstrates that significant efficiency gains and emission reductions can be achieved by optimizing existing processes. The study's authors concluded that the potential ecological and economic benefits "led to the conclusion that converter gas is strongly recommended as fuel for a tunnel furnace"1 . The main practical hurdle is ensuring that gas burners are modified or designed to provide the same amount of energy input when operating on the lower-calorific-value converter gas as they did with natural gas1 .
From an environmental perspective, this practice is a clear win. It exemplifies the core principle of a circular economy, reducing waste and maximizing resource efficiency. For the steel industry, it strengthens economic resilience by lowering operational costs and reducing dependence on volatile external energy markets.
This ingenious solution proves that what we often label as "waste" can be a hidden resource. By looking at their own operations with a fresh perspective, steelmakers are finding that the key to a greener, more profitable future has been floating up their smokestacks all along.
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